Resigella, LOEBLICH & TAPPAN, 1984

Gooday, A. J., Todo, Y., Uematsu, K. & Kitazato, H., 2008, New organic-walled Foraminifera (Protista) from the ocean’s deepest point, the Challenger Deep (western Pacific Ocean), Zoological Journal of the Linnean Society 153 (3), pp. 399-423 : 406-416

RESIGELLA LOEBLICH & TAPPAN, 1984

Resigella Loeblich & Tappan, 1984, p. 1158

Type species: Nodellum moniliforme Resig, 1982 .

Diagnosis: Test <1 mm in length, consisting of symmetrically oval proloculus followed by 1–6 approximately droplet-shaped to subcylindrical chambers separated by distinct, regular constrictions or short stolons. Chambers arranged in linear sequence along straight, gently arcuate or occasionally slightly sinuous axis. Proximal end (base) of initial chamber (proloculus) either smoothly rounded or interrupted by pocket-like invagination. Test wall rigid, fairly brittle, orange or yellowish-brown in colour and more or less transparent. Wall mainly organic but incorporating some fine, adhering particles, in some species concentrated in constrictions between segments. Some or all chambers contain stercomata. (Slightly modified after Gooday et al., 2008).

Remarks: In the type species, Resigella moniliforme , the base of the proloculus has a pocket-like invagination ( Gooday et al., 2008) that is not present in the two Challenger Deep species described below. The taxonomic significance of this feature is unclear and it is possible that Resigella should be split into two genera based on its presence or absence. However, because of their general morphological similarity, we prefer to retain the three species in one genus for the present.

RESIGELLA LAEVIS SP. NOV.

FIGS 8–10

Resigella- like form 1. Todo, 2003, pl. 6, fig. 5 ‘Multichambered organic-walled allogromiid similar to Resigella ’. Todo, Kitazato, Hashimoto, Gooday, 2005, fig. 1B.

Diagnosis: Species of Resigella with test comprising gently curved series of 3–4 (occasionally five) elongate, droplet-shaped to subcylindrical chambers, separated by distinct constrictions. Initial chamber (proloculus) with smoothly rounded proximal end lacking basal invagination. Final chamber somewhat asymmetrical with round terminal aperture. Test wall transparent, pale yellowish in colour, mainly organic but incorporating some clay particles. Surface of proloculus smooth at submicrometre scale. Surfaces of later chambers covered in mass of short, branching, finger-like projections up to 0.1 Mm long, visible only by SEM.

Types: The type specimens are deposited in Tokyo and London under reg. nos. MPC-02710 (holotype), MPC- 02711-02715 (five paratypes) and ZF 5170 (two paratypes)

Other material examined: 78 specimens. Derivation of name: Latin laevis , smooth, referring to the appearance of the test surface under the light microscope

Description

Test morphology: The test usually consists of 3–4 elongate chambers (two out of 86 specimens have five chambers) joined in a gently curved, linear series and separated by distinct necks ( Fig. 8 ). The final chamber is elongate and has a slightly asymmetrical shape with one side being more or less straight and the other side gently curved. The first one or two chambers (including the proloculus) are usually approximately symmetrical and oval to fusiform in shape with curved sides. Occasional specimens have an additional swelling between two of the main chambers ( Fig. 8D ). Detailed dimensions are given in Table 2. The test ranges from 120 to 266 Mm in length. The chambers generally increase in length from the proximal to the distal end of the test. The proloculus and the adjacent chamber (numbers 1 and 2 from the proximal end) are similar in size, 13–49 Mm long and 11–24 Mm wide, chamber 3 is 28–76 Mm long and 15–35 Mm wide, and chamber 4, which is always the longest, is 46–111 Mm long and 20–38 Mm wide.

Aperture: The aperture is located at the bluntly pointed end of the final chamber ( Fig. 9A ). In specimens examined by SEM, it is a simple opening, 5–7 Mm across, with a slightly puckered rim ( Fig. 10A, B, F ). The aperture sometimes extends into a flimsy, organic, tubular structure.

Wall structure and composition: The wall is mainly organic and transparent with a distinct brownish tinge and completely smooth with a shiny surface when viewed by light microscopy. When examined by SEM, the surface of the proloculus has a slightly crumpled appearance but is otherwise smooth at magnifications up to 10 000¥ ( Fig. 9B, F, G ). The surfaces of subsequent chambers, however, resolve at magnification of 10–15 000¥ into a mass of short, branching, finger-like projections similar to those observed in Nodellum aculeata . They clearly arise from the underlying test wall. Individual branches are up to about 0.10 Mm (100 nm) long and no more than 0.015 Mm (15 nm) wide. The density of these projections is not uniform across along the test. They are fairly sparsely developed near the terminal aperture of at least one specimen ( Fig. 10C, D ). Where the proloculus joins the second chamber, there is a regular, zig-zag interdigitation of the two types of surface ( Fig. 9B, C ). Flat plate-like features that often merge with the projections ( Fig. 9E ), and scale-like structures around the aperture ( Fig. 10B ), are interpreted as clay particles (see below). The wall appears fairly rigid and tends to crack or split when damaged mechanically ( Fig. 10F ). It is ~0.25–0.55 Mm thick, becoming thicker near the aperture. Broken sections display no obvious internal structure ( Fig. 10G ).

EDS analyses of the proloculus and later chambers reveal the presence of Fe, Mg, Al, Si and Ca. Peak sizes are variable, but those for Mg, Al, Si and Ca tend to be higher on later chambers whereas Fe peaks tend to be higher on the proloculus. These analyses suggest that clay particles are present on later chambers, and probably also on the proloculus, and that the organic wall contains iron.

Test interior: In live individuals, all or some of the chambers are filled, or partially filled, with brownish stercomata ( Fig. 8 ). Occasionally, an obvious cytoplasmic mass is located just inside the aperture of the final chamber ( Fig. 8O ). It is sometimes separated from the stercomata by a thin organic partition ( Fig. 8M ). In dead individuals, the stercomata become greyish in colour and break down into finely granular material.

Remarks: Resigella laevis lacks the pocket-like invagination at the base of the proloculus that is always present in R. moniliforme , the type species of Resigella . It is also smaller than the type species (usually <250 Mm in length compared with 280–670 Mm) and the chambers are much more elongate, sometimes subcylindrical, rather than droplet-shaped. Another difference is that the new species lacks the accumulations of agglutinated particles that The figures in parentheses are outliers.

SE = standard error.

are developed in the constrictions between the chambers in R. moniliforme .

Resigella- like form 1 of Todo (2003: pl. 6, fig. 5) from Stn NK- 3 in the Japan Trench (7761 m water depth) may be conspecific with R. laevis . The only difference is that the constrictions between the chambers are somewhat less prominent than in the Challenger Deep specimens. Resigella- like form 2 of Nozawa (2005: pl. 6, fig. C) from the abyssal Kaplan East site in the Equatorial Pacific (4100 m depth) also resembles the new species, but has a much more pronounced constriction between the two chambers (the specimen may be incomplete). A similar, threechambered, organic-walled Resigella- like form from 7800 m in the Atacama Trench is illustrated by Sabbatini et al. (2002: pl. 1, fig. 2) and Gooday et al. (2004: fig. 5D). However, the final chamber has a more symmetrically oval shape, and the proloculus is more inflated than in R. laevis . It probably represents a distinct species.

RESIGELLA BILOCULARIS SP. NOV.

FIGS 11–13

Diagnosis: Species of Resigella with test comprising two oval to droplet-shaped chambers arranged on a linear axis and separated by short neck. Initial chamber (proloculus) with rounded or somewhat pointed proximal end which lacks basal invagination. Test wall basically organic and transparent; second chamber distinctly brownish-yellow in colour. Surface of proloculus smooth at submicrometre scale, sometimes with partial veneer of plate-like clay particles. Second chamber with variable number of small, irregularly arranged mineral grains concentrated in proximal part; other parts of wall with flat, scale-like features (probably clay particles) merging into meshwork of bar-like elements, visible only by SEM.

Types: The type specimens are deposited in Tokyo and London under reg. nos. MPC-02697 (holotype), MPC-02696 (one paratype) and ZF 5171 (four paratypes)

Other material examined: 15 specimens.

Derivation of name: The name refers to the consistently bilocular nature of the test.

Description

Test morphology: The test consists of two globular chambers, the initial chamber (proloculus) being about half the size of the second chamber ( Fig. 11 ). The initial chamber is more or less symmetrically oval, often with a somewhat pointed proximal end. The second chamber is droplet-shaped, widest behind the mid point, and tapers towards the slightly truncated apertural end. The initial chamber is joined to the second chamber by a very short, narrow neck. The overall length of the test is 107–190 Mm (usually 164–190 Mm; mean 167 Mm, SE 25.0 Mm). The first chamber measures 50–85 Mm (mean 65 Mm, SE 11.7 Mm) long and 28–53 Mm (mean 43 Mm, SE 6.6 Mm) wide. The second chamber measures 70–133 Mm (usually 106–133 Mm; mean 112 Mm, SE 18.2 Mm) long and 38–93 Mm (usually 54–93 Mm; mean 67 Mm, SE 18 Mm) wide.

Aperture: The aperture is located at the distal end of the second chamber ( Fig. 11D, G ). In some specimens examined by light microscopy, it is a simple, circular opening; in others it is produced slightly into a very short, delicate neck composed of transparent organic material. One specimen examined by SEM has a circular opening, ~15 Mm diameter, enclosing a rather complex organic structure ( Fig. 13A ). The inner part of this structure (~10–11 Mm diameter) has vague, linear features radiating from a central cluster of raised lips within which the aperture presumably lies. This probably corresponds to the delicate neck sometimes visible by light microscopy

Wall structure and composition: The test wall is basically organic, transparent, with a distinct, brownishyellow colour in transmitted light. The colour is usually more evident in the second chamber, which has a thicker wall than the first chamber. A deposit of finely agglutinated material, visible by light microscopy, is often loosely attached to part of the wall of the second chamber ( Fig. 11D, G ), but is variably developed and in some specimens seems to be entirely absent. Where present, it typically becomes thicker away from the aperture, particularly in front of the join between the first and second chambers. Viewed in the SEM, the agglutinated layer is composed of a mixture of mostly angular mineral grains, the largest of which are 1.0–1.5 Mm in size ( Fig. 12E ).

The surface of the larger second chamber has a complex appearance when viewed by SEM ( Figs 12F–H , 13F ). It includes flat areas of varying sizes (up to ~1 Mm but usually smaller), some of them scale-like. These features may be clay particles (see below). They merge at their edges into a tangled meshwork of bar-like elements, the individual bars being 0.01–0.02 Mm (10–20 nm) in width. The smaller first chamber has a smooth surface, sometimes with a partial coating of plate-like grains a few micrometres in diameter and some flake-like features at submicrometre scale. Broken cross-sections of the organic part of the wall are ~0.20–0.35 Mm (200–350 nm) thick and appear featureless, apart from irregularities probably related to fracturing ( Fig. 13D ).

EDS analyses of the proloculus reveal strong Al and Si peaks suggesting that the plate-like grains are clay minerals. Analyses of more equidimensional grains on the second chamber indicate a variety of compositions. A strong peak for Si with additional peaks for Mg and Al suggest that some grains are clay minerals. Other particles have high concentrations of Ca and S. The organic part of the wall of both chambers yields a strong Fe peak, a weaker Si peak and small peaks for Mg and Al.

Test interior: The initial chamber is usually empty. In live individuals, the second chamber contains stercomata and protoplasm. The protoplasm forms a distinct mass just inside the aperture and behind this is an area occupied by stercomata. In one of the specimens, there is a thin partition between the two parts of the chamber ( Fig. 11G ).

Remarks: The droplet-like second chamber of Resigella bilocularis is remarkably similar in shape to the later chambers of R. moniliforme (illustrated by Gooday et al., 2008: fig. 9). The test surface of both species is often characterized by an irregularly developed sprinkling of agglutinated particles that becomes thicker towards the proximal end of the later chambers. However, the two-chambered test of R. bilocularis distinguishes it from both R. moniliforme (up to six chambers) and R. laevis (3–4 chambers). The chambers are also much more globular than in R. laevis , and there is no trace of the basal invagination of the proloculus, which is a consistent feature of R. moniliforme .

Brownish, bilocular, organic-walled tests resembling Resigella bilocularis are an occasional but widespread component of abyssal foraminiferal assemblages, having been reported in the North and Equatorial Pacific ( Gooday et al., 2004; Nozawa, 2005), the Weddell Sea ( Cornelius & Gooday, 2004) and north-east Atlantic ( Gooday, Carstens & Thiel, 1995). These abyssal specimens are generally rather smaller (120–155 Mm) than those from the Challenger Deep but in other respects are similar. However, in the absence of molecular data, we hesitate to regard them as conspecific. Bilocular morphotypes of Resigella are not represented in the Atacama Trench ( Sabbatini et al., 2002).

Figures

Figure 8. Resigella laevis sp. nov. Transmission light micrographs of specimens on open slides in glycerol. A, holotype, reg. no. MPC-02710. B–G, paratypes, reg. nos. MPC-02711-02715. H, I, paratypes, reg. nos. ZF 5170. J–O, other specimens; M shows detail of final chamber with partition in front of stercomata; O shows detail of final chamber with mass of cytoplasm in front of stercomata. All scale bars = 50 Mm except where indicated otherwise.

Figure 9. Resigella laevis sp. nov. Scanning electron micrographs. A, general view of test. B, proloculus. C, detail of interdigitated border between smooth organic surface of proloculus and highly ornamented organic surface of later chambers; boxes indicate areas shown in detail in D and F. D, E, surface of chamber immediately in front of proloculus showing mass of finger-like projections; the flat features are probably clay particles. F, G, surface of proloculus.

Figure 10. Resigella laevis sp. nov. Scanning electron micrographs. A, B, aperture. C, D, surface of test near aperture showing relatively sparse development of finger-like projections. E, general view of test. F, aperture. G, broken section of wall.

Figure 11. Resigella bilocularis sp. nov. Transmission light micrographs of specimens on open slides in glycerol. A, holotype, reg. no. MPC-02697. B, paratype, reg. no. MPC-02696. C, D, general view and detail of specimen illustrated by SEM in Figure 12A–B. E, general view of specimen illustrated by SEM in Figure 13E–F. G, specimen with delicate partition in front of stercomata. H, paratype, reg. no. ZF 5171. I, small specimen with clearly developed neck between the two chambers. All scale bars = 50 Mm.

Figure 12. Resigella bilocularis sp. nov. Scanning electron micrographs. A, general view; note collapsed initial chamber. B, detail of same specimen showing agglutinated coating of organic wall; note that the grains become more prominent towards proximal part of chamber. C–H, damaged specimen; the initial chamber has been lost. C, general view; areas within boxes are shown in more detail in E–H. D, surface of proximal part of chamber showing agglutinated grains. E, surface towards posterior end of chamber showing agglutinated grains and smoother, intervening areas; box indicates area shown in detail in F. F, detail of organic wall with mesh-like structures and a few flat areas. G, H, surface towards distal part of chamber showing smooth, flake-like features separated by areas with a fine, mesh-like structure. The flake-like features in F–H are probably clay particles.

Figure 13. Resigella bilocularis sp. nov. Scanning electron micrographs. A, aperture of specimen shown in Figure 12C. B, general view of specimen with intact intial chamber and broken second chamber. C, D, broken cross-section of test wall showing organic layer overlain by agglutinated grains. E, F, general view of test and detail of organic surface with flake-like features (probably clay particles) separated by mesh-like structures.